1. Field of the Invention
The present invention relates to a communication method applicable to the orthogonal frequency division multiplex system (OFDM system) and a receiving apparatus for receiving a signal according to the communication method.
2. Description of the Related Art
For a communication method suitable for a mobile communication such as a wireless telephone system or the like, a multicarrier communication method called Orthogonal Frequency Division Multiplexing (OFDM system) has been proposed. This system is such that a plurality of subcarriers are arranged at a predetermined frequency interval within one transmission band and data is scattered over the respective subcarriers to modulate them for transmission. In this case, on a transmitting side, transmitting data in the form of a time sequence is orthogonal-transformed to a multicarrier signal at a predetermined frequency interval by a fast Fourier transform or the like. On a receiving side, a received multicarrier signal is subjected to the inverse transform of that in transmission for obtaining received data.
The transmitted signal according to the OFDM system has an advantage in that even if there is a multipath a good transmission characteristic is ensured, so that it is particularly suitable for the mobile communication such as the wireless telephone system or the like.
When such multicarrier signal is received, it is difficult to detect a frequency offset of the received signal. Specifically, when the multicarrier signal in which subcarriers of a predetermined number are provided in one transmission band, for example, is transmitted in a plurality of continuous transmission bands, it is difficult for the reception side to easily determine which range of the subcarriers from one transmission band. Especially, in order to increase the transmission efficiency, a frequency interval between the adjacent subcarriers is very narrow (e.g., an interval of several kHz) in the communication of this kind, which makes it difficult to precisely detect the frequency offset.
In order to solve this disadvantage, it can be considered that the transmission side transmits a specific symbol by using a subcarrier at a specific position in one transmission band and the reception side corrects an offset of a reception frequency with reference to the subcarrier in which the reception side receives the specific symbol. However, when such a specific symbol is transmitted, the period of data transmission is reduced to that extent, which reduces the transmission capacity.